1. Field of the Invention
This invention relates to a lighting apparatus which, with a light source, reflector, and lens et al. combined, projects a parallel-running light to an intended direction efficiently.
2. Prior Art
In a display device especially, the projection type liquid crystal display, which, receiving a light projected on the liquid crystal panel thereof, project to a screen the image appearing in the panel enlarging it with appropriate optical system, the lighting apparatus therefor was required to project a light beam or rays of lights running parallel all perpendicularly to the surface of each element of liquid crystal panel to conform to the characteristics of the panel.
As the lighting apparatus to obtain such object, several structures have been proposed:
One of the apparatus, as shown in FIG. 7, consists of a point light source 1 (for example, a tungsten halogen lamp, metal halide lamp or short arc type xenon lamp) and a paraboloid type reflector 3 to surround and keep at its focal point A the light source 1, the section of the reflector by a plane passing the optical axis 2 forming a parabola. A part of the light emitted by the light source is reflected by the paraboloid reflector 3 to project light beam on a liquid crystal panel 4 or the object to be lighted.
Another apparatus, as shown in FIG. 8, is a combination of a light source 1, spherical reflector 6, and a converging lens 7, and the light source 1 is placed at the coinciding focal points B of the spherical reflector 6 and the converging lens 7. A part of the light of the light source 1 is reflected by the spherical reflector 6 to pass again the focal point B, and, with the other light from the source, proceeds to the converging lens 7, to project light beam on the liquid crystal panel 4 (Publication of Japanese Patent Application No. Sho 59-42404).
The third apparatus is constructed by a light source 1, a ellipsoidal reflector 9, and a converging lens 10, so arranged that the light source 1 is placed at one focal point C of the ellipsoidal reflector 9 and the converging lens has its focal point at the second focal point D of the ellipsoid. With this structure, most of the light of the light source 1 is reflected by the ellipsoidal reflector 9 to converge at the second focal point D, to proceed to the converging lens 10, and to be projected on the liquid crystal panel 4 as a light beam (Publication of Japanese Patent Application, No. Hei 1-25046).
Any of the above apparatus arrange the light source at the focal point of a reflector of conicoid, and a part of the light of the source is reflected by the reflector to proceed to the liquid crystal panel directly or through a converging lens, performing efficient use of light.
In the projection type liquid crystal display, a liquid crystal panel of rectangle or square of about 3 diagonal is used at the moment. To light whole surface of the liquid panel efficiently, it is, of course, necessary for the light beam to have section at least the same with or larger than the liquid crystal panel.
Efficient projection of light on the liquid crystal panel is obtained by making the section of the light beam to be the same as the shape of the panel (Japanese Patent Application Laid-Open, No. Hei 4-7503). However, the complicated structure of the reflector is not practical. And, in the lighting apparatus in practical use for the projection type liquid crystal image display the light beam 14 projecting to the panel 13, through ellipsoidal reflector 12 is of circular or approximately circular section, (as shown by the two-dot dash line in FIG. 11) as a result of the performance of the constructing optical elements.
The liquid crystal panel 13 is, as described above, rectangular or square and it is arranged so as the panel is perpendicular to the optical axis 14 of the beam from the reflector 12 and is inscribed to-the circular section of the beam.
For the efficient lighting of the liquid crystal panel, as is shown in FIG. 10 and FIG. 11, it is noted that the light is projected within the range of h as shown by the hatching. While the light beam is of circular section shown by H in FIG. 10 and FIG. 11, the remaining part of the light (H-h) was not used.
Also it is known, that the light emittion of the metal halide lamp as used as the light source 11 consists of a line spectrum of mercury at the middle of the arc and a strong spectrum of rare earth element involved in the lamp at the outer part, so that, this color division between the center and the outer part brings the unevenness of color between the center and outer part of the liquid crystal panel, resulting in the unevenness of color on the screen.